Oracle PL/SQL for DBAs

The Effects of Key Length

My lock combination is the digital equivalent of sensitive data. If an intruder wants to crack the encrypted key, 10,000 iterations to guess the code is trivial—he’ll be able to crack it in under a second. What if I use an alphanumeric key instead of an all-numeric one? That gives 36 possible values for each character of the key, so the intruder will have to guess up to 36⁴, or 1,679,616, combinations—more difficult than 10,000, but still not beyond reach. The key must be strengthened, or “hardened,” by making it longer than 4 characters. Table 4-1 shows how the maximum number of guesses required increases with the increase in the key length. Therefore, the secret to hardening the key is to increase the length of the key.

Table 4-1. Alphanumeric key length and maximum number of guesses required to crack the key

Key length	Maximum number of guesses required
4	1,679,616
5	60,466,176
6	2,176,782,336
7	78,364,164,096
8	2,821,109,907,456
9	101,559,956,668,416
10	3,656,158,440,062,976

Remember that computers think in terms of bits and bytes (i.e., binary numbers), not alphanumeric characters. The possible values of a key position are 0 and 1, so the 10-digit key needs only 2¹⁰, or 1024, combinations, an extremely easy number to handle. Practically speaking, a key must be much longer. The length of a key is described in bits, so a key of 64 numbers is said to be of 64-bit. Table 4-2 shows the relationship between key length and number of guesses ...